Supplementary services are improvements and supplements to basic services in mobile communications, and mainly include seven categories: call identification, call forwarding, call completion, multiparty call, call barring, charging notification, and closed user group. For example, a call waiting service is one of supplementary services of a voice call service (basic service). A function of the call waiting service is as follows: When a mobile phone user is on a call, and another call is initiated to the user, in this case, a party that initiates the new call is set to wait, and the user on a call may select whether to answer the new incoming call, or reject or neglect the new incoming call.
However, with a generational shift of a communications network, an implementation manner of the supplementary services in each generation of communications network is not the same. For example, in a conventional 2G (GSM, CDMA, and the like) or 3G (WCDMA and the like) network, a voice call service and its corresponding supplementary service are borne by a circuit switched domain (that is, CS domain, Circuit Switch), and service configuration of the voice call service is stored in a subscriber configuration database (that is, HLR, Home Location Register, home location register) on a network side in a core network. When the corresponding supplementary service is conducted, a mobile switching center (MSC, Mobile Switching Center) reads the corresponding service configuration. However, in an emerging LTE (Long Term Evolution, Long Term Evolution system, that is, a 4G network) network, a voice call uses a VoLTE (Voice over LTE Network) technology, and is borne by an IMS (IP Multimedia Subsystem, multimedia subsystem) domain of the LTE network. Service configuration of a VoLTE service is stored on a terminal. When a user moves from an area covered by the LTE network to an area covered by the conventional 2G or 3G network and a handover occurs, a case in which call supplementary service configuration is not synchronous occurs, thereby requiring the user to manually re-perform configuration. Therefore, a capability of adapting to multiple communications networks in a process of performing call supplementary service configuration in a conventional technology is relatively low.